Gas turbine engine compressors having optimized stall enhancement feature configurations and methods for the production thereof

ABSTRACT

Multistage gas turbine engine (GTE) compressors having optimized stall enhancement feature (SEF) configurations are provided, as are methods for the production thereof. The multistage GTE compressor includes a series of axial compressor stages each containing a rotor mounted to a shaft of a gas turbine engine. In one embodiment, the method includes the steps or processes of selecting a plurality of engine speeds distributed across an operational speed range of the gas turbine engine, identifying one or more stall limiting rotors at each of the selected engine speeds, establishing an SEF configuration in which SEFs are integrated into the multistage GTE compressor at selected locations corresponding to the stall limiting rotors, and producing the multistage GTE compressor in accordance with the optimized SEF configuration.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending U.S. application Ser. No.14/612,404, filed Feb. 3, 2015.

TECHNICAL FIELD

The present invention relates generally to gas turbine engines and, moreparticularly, to gas turbine engine compressors having optimized stallenhancement feature configurations and to methods for the productionthereof.

BACKGROUND

The compressor section of a Gas Turbine Engine (GTE) often includesmultiple axial compressor stages positioned in succession. Each axialcompressor stage typically contains a rotor disposed immediatelyupstream of a stator. The compressor rotors are essentially bladedwheels, which are surrounded by a tubular casing or shroud. Eachcompressor rotor may be mounted to a shaft of the GTE. During operation,the compressor rotors rotate along with the shaft to compress airflowreceived from the GTE's intake section. The final axial compressor stagedischarges the hot, compressed air, which can be supplied directly tothe engine's combustion section for mixture with fuel and subsequentignition of the fuel-air mixture. Alternatively, the airflow dischargedby the final axial compressor stage can be fed into a centrifugal orradial compressor stage, which further compresses and heats the airflowprior to delivery to the engine's combustion section.

As compressor pressure ratios improve, so too does overall GTEperformance potential. Several different approaches have traditionallybeen employed to improve compressor pressure ratios. These traditionalapproaches include increasing the compressor stage count, increasing theaerodynamic loading of the compressor, and increasing the rotationalspeed range over which the compressor section operations. Each of theforegoing approaches is, however, associated with a correspondingtradeoff or penalty. For example, increasing the number of compressorstages adds undesired length, weight, and cost to the GTE. Additionally,increasing the number of compressor stages can degrade performancematching for off-design GTE operation. Increasing the aerodynamicloading of the compressor often negatively impacts compressor stallmargin. Finally, increasing the rotational speed range over which theGTE operates typically reduces compressor efficiency and can shorten theoperational lifespan of the engine components.

BRIEF SUMMARY

Methods for producing multistage gas turbine engine (GTE) compressorshaving optimized stall enhancement feature (SEF) configurations areprovided. The multistage GTE compressor includes a series of axialcompressor stages each containing a rotor mounted to a shaft of a gasturbine engine. In one embodiment, the method includes the steps orprocesses of selecting a plurality of engine speeds distributed acrossan operational speed range of the gas turbine engine, identifying one ormore stall limiting rotors at each of the selected engine speeds, andestablishing an optimized SEF configuration in which SEFs are integratedinto the multistage GTE compressor at selected locations correspondingto the stall limiting rotors. The multistage GTE compressor is thenproduced in accordance with the optimized SEF configuration. In certaincases, the optimized SEF configuration can be established to include afirst type of stall enhancing feature disposed at a locationcorresponding to a first stall limiting rotor and to include a second,different type of stall enhancing feature disposed at locationcorresponding to a second stall limiting rotor. In such embodiments, thefirst type of stall enhancing feature may be casing treatment featuresdisposed at a location circumscribing the leading rotor.

In another embodiment wherein the series of axial compressor stagescontains a total number of rotors equal to n_(total), the methodincludes the step or process of producing the multistage GTE compressorto include SEFs applied at selected locations corresponding to a subsetof rotors equal to n_(enhanced). The multistage GTE compressor isfurther produced such that 2≤n_(enhanced)<n_(total). Additionally, theSEFs are applied to at least one forward compressor stage and to atleast one aft compressor stage of the multistage GTE compressor.

Multistage GTE compressors having optimally-positioned stall enhancementfeatures are further provided. In one embodiment, the multistage GTEcompressor includes an engine casing, a shaft mounted in the enginecasing for rotation about a rotational axis, and a series of axialcompressor stages each containing a rotor mounted to the shaft andsurrounded by the engine casing. A plurality of SEFs is integrated intothe series of axial compressor stages at locations corresponding to aselected subset of rotors. The total number of rotors included withinthe series of axial compressor stages is equal to n_(total), while thenumber of rotors included within the selected subset of rotors is equalto n_(enhanced) such that 2≤n_(enhanced)<n_(total).

BRIEF DESCRIPTION OF THE DRAWINGS

At least one example of the present invention will hereinafter bedescribed in conjunction with the following figures, wherein likenumerals denote like elements, and:

FIG. 1 is a cross-sectional schematic of a multistage Gas Turbine Engine(GTE) compressor having an optimized stall enhancing feature (SEF)configuration and produced in accordance with an exemplary embodiment ofthe present invention;

FIG. 2 is a detailed cross-sectional view of a first region of themultistage GTE compressor shown in FIG. 1 at which SEFs in the form ofcasing treatment features have been selectively applied;

FIG. 3 is a detailed cross-sectional view of a second region of themultistage GTE compressor shown in FIG. 1 at which SEFs in the form ofupstream injection features have been selectively applied;

FIG. 4 is a flowchart setting-forth an exemplary method for optimizingGTE performance by selectively applying SEFs to a multistage GTEcompressor, such as the multistage GTE compressor shown in FIG. 1;

FIG. 5 is a compressor performance map that may be generated during theexemplary optimization method set-forth in FIG. 4 prior to the selectiveapplication of SEFs to a virtual or physical model of the multistage GTEcompressor; and

FIG. 6 is a compressor performance map that may be further generatedduring the exemplary optimization method set-forth in FIG. 4 after theselective application of SEFs to the compressor model.

DETAILED DESCRIPTION

The following Detailed Description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding Background or the following DetailedDescription.

The following describes embodiments of a method for improving theperformance of a multistage GTE compressor through the selectiveapplication of stall enhancing features (SEFs) to the compressor. Asappearing herein, the term “stall enhancing features” and itscorresponding acronym “SEFs” refer generally to any structural featureor device suitable for usage within a multistage GTE compressor toincrease the stall margin of a compressor rotor, such as an axialcompressor rotor. Stall enhancing features that are formed in orotherwise integrated into the engine casing at a location surrounding arotor (and, perhaps, extending for some distance beyond the rotor in aforward and/or an aft direction) are referred to herein as “casingtreatment features.” A non-exhaustive list of casing treatment featuresincludes grooves or channels formed in the interior of the engine casingor rotor shroud, honeycomb structures, recirculating treatments, suctiondevices, blowing devices, active clearance control devices, and plasmaflow control devices. Stall enhancing features that inject pressurizedairflow upstream of a rotor (specifically, in the rotor's upstream flowfield) are referred to herein as “upstream injection features.” Upstreaminjection features include, but are not limited to, stator hub flowinjection features, which direct pressurized airflow into the main flowpath at a location proximate the hub of the stator immediately upstreamof the rotor targeted for stall margin increase.

The term “selective application” is utilized herein to indicate thatSEFs are not applied globally across the multistage GTE compressor, butrather integrated into the compressor at a limited number of locationscorresponding to certain “stall limiting” rotors. In this regard, thepresent inventors have determined that the global application of SEFsacross all compressor stages of a multistage GTE compressor can resultin a performance penalty for a subset of the compressor stages,especially when the multistage GTE compressor includes a relatively highnumber of axial compressor stages. Additionally, the global applicationof SEFs across all compressor stages of a multistage GTE compressor canadd undesired cost and complexity to the manufacturing process utilizedto produce the compressor. At the same time, the potential increase incompressor pressure ratios may not be fully realized by the exclusiveapplication of SEFs to a single stage (e.g., the first compressor stage)or rotor of a multistage GTE compressor. Consequently, there exists anongoing need to provide methods for optimizing compressor performancethrough the selective application of SEFs to a multistage GTEcompressor. Embodiments of such a method are described herein.

For the purposes of explanation, the following will describe embodimentsof the method for optimizing compressor performance in conjunction anexemplary multistage GTE compressor 10, as schematically illustrated inFIG. 1. The following description notwithstanding, it is emphasized thatmultistage GTE compressor 10 is shown by way of non-limiting exampleonly and that embodiments the compressor optimization method can becarried-out for any multistage GTE compressor having at least two axialcompressor stages. As can be seen in FIG. 1, multistage GTE compressor10 includes an inlet 12, an outlet 14, and a number of axial compressorstages 16, which are positioned in flow series between inlet 12 andoutlet 14. Each compressor stage 16 includes an axial compressor rotor18 followed by a compressor stator 20. In the illustrated example,multistage GTE compressor 10 includes a total of six compressor stages16, which are identified as stages 16(a)-16(f). The compressor rotorsand stators are also individually labeled in keeping with thisconvention such that the rotor and stator included in compressor stage16(a) are identified by reference numerals “18(a)” and “20(a),”respectively; the rotor and stator included in compressor stage 16(b)are identified by reference numerals “18(b)” and “20(b),” respectively;the rotor and stator included in compressor stage 16(c) are identifiedby reference numerals “18(c)” and “20(c),” respectively; and so on.Additionally, an Inlet Guide Vane (IGV) assembly 22 is furtherpositioned immediately upstream of the first axial compressor stage16(a).

Compressor stages 16 are surrounded by a shroud or engine casing 24. Itwill be appreciated that, as are the other components of multistage GTEcompressor 10, engine casing 24 is generally axisymmetric about thecenterline or rotational axis 28 of the gas turbine engine. Enginecasing 24 thus has a generally tubular or annular shape when viewed inthree dimensions. Engine casing 24 and the other non-illustratedcomponents of multistage GTE compressor 10 are included in the staticinfrastructure of the GTE core. Compressor stators 20 are bolted orotherwise fixedly attached the static engine infrastructure such thatstators 20 do not rotate during engine operation. In contrast,compressor rotors 18 are fixedly mounted to a shaft 26 (e.g., utilizingfriction drive or curvic-type couplings) and rotate in conjunctiontherewith about rotational axis 28. Although not visible in theillustrated schematic, the blade tips of each compressor rotor 18 areseparated from the inner circumferential surface of engine casing 24 bya small annular clearance or gap. Furthermore, although only a singleshaft 26 is shown in FIG. 1, it will be appreciated that the enginecontaining multistage GTE compressor 10 can include any practical numberof shafts in further embodiments. Finally, while shown to include onlyaxial compressor stages in the illustrated example, compressor 10include an additional radial or centrifugal compressor stage downstreamof the final axial compressor stage 16(f) in further embodiments. Inthis case, the centrifugal compressor stage may also be evaluatedutilizing the process or method described below and also considered forthe potential application of stall enhancing features. Specifically, insuch embodiments, it can be determined whether the impeller contained inthe centrifugal compressor stage is a “stall limiting rotor” of the typedefined below and, if the impeller is so identified, stall enhancingfeatures can be applied around or immediately upstream of the impellerto improve its stall margin at one or more selected engine speeds, asdescribed below.

In accordance with embodiments of the present invention, SEFs areapplied to or integrated into multistage GTE compressor 10 at selectedlocations corresponding to a number of stall limiting rotors. Rotor areidentified herein as “stall limiting” when, absent the stall-boostingeffect of the below-described SEFs, the rotor sets stall of compressor10 at an undesirably low level for at least one engine speed. In theexemplary embodiment shown in FIG. 3, multistage GTE compressor 10includes three such stall limiting rotors: (i) rotor 18(a) contained inthe first or leading axial compressor stage 16(a), (ii) rotor 18(e)contained in the fifth axial compressor stage 16(e), and (iii) rotor18(f) contained within the sixth and final (trailing) axial compressorstage 16(f). As will be described more fully below, SEFs are integratedinto multistage GTE compressor 10 at selected locations corresponding tostall limiting rotors 18(a), 18(e), and 18(f). In the exemplaryembodiment shown in FIG. 1, these locations are generically representedby cross-hatched regions 30, 31, and 32 corresponding to rotors 18(a),18(e), and 18(f), respectively.

A given SEF (or group of SEFs) is considered to be positioned at alocation “corresponding to” a stall limiting rotor when the SEF ispositioned to have a direct boosting effecting on the stall margin ofthe targeted rotor. The relative positioning between a given SEF and itscorresponding stall limiting rotor will vary in conjunction with SEFtype. For example, in an embodiment wherein one or more of the SEFsassume the form of casing treatment features, the casing treatmentfeatures will typically be integrated into the engine casing atlocations surrounding one or more stall limiting rotors and, perhaps,extending beyond each stall limiting rotor by some amount in a forwardand/or aftward direction. With continued reference to FIG. 1,cross-hatched regions 30 and 32 may be considered to represent casingtreatment features formed in engine casing 24 at a locations surroundingor circumscribing stall limiting rotors 18(a) and 18(f), respectively.In contrast, in an embodiment wherein one or more of the SEFs assume theform of upstream injection features, the upstream injection features canbe disposed at any location upstream or forward of the stall limitingrotor, while remaining within the rotor's flow field. An example of thisis shown in FIG. 1 at cross-hatched region 31, which represents upstreaminjection features disposed forward of stall limiting rotor 18(e).

Multistage GTE compressor 10 can be described as containing threeforward compressor stages 16(a)-(c) and three aft compressor stages16(d)-(f). As appearing herein, the term “forward compressor stage(s)”refers to the compressor stage(s) upstream of the median compressorstage when the compressor includes an odd number of compressor stages orupstream of a plane (orthogonal to rotational axis 28) having an equalnumber of compressor stages on its opposing sides when the compressorcontains an even number of compressor stages. Conversely, the term “aftcompressor stage(s)” refers to the compressor stage(s) downstream of themedian compressor stage when the compressor includes an odd number ofcompressor stages or downstream of a plane having an equal number ofcompressor stages on its opposing sides when the compressor includes aneven number of compressor stages. The number of rotors identified as“stall limiting” and targeted by the selective application of SEFs willvary amongst embodiments. However, in many embodiments, the compressorwill include at least one forward compressor stage and at least one aftcompressor stage to which SEFs are applied in accordance with the methoddescribed below. In further embodiments, SEFs can be added to fewer orgreater number of compressor stages, providing that SEFs are applied toat least two axial compressor stages included within the multistage GTEcompressor, but less than the total number of axial compressor stagesincluded therein. In such embodiments, the following equation maypertain: 2≤n_(enhanced)<n_(total), wherein n_(total) is the total numberof rotors included within the axial compressor stages, and wherein theSEFs are applied at selected locations corresponding to n_(enhanced)number of the rotors.

FIG. 2 illustrates region 30 of compressor 10 in an embodiment whereinthe SEFs are realized as a number of circumferential channels or grooves34 formed in the interior surface of engine casing 24. Grooves 34surround or circumscribe rotor 18(a) and are located radially outboardof the tips of the rotor blades 36 (one of which is partially shown inFIG. 2). The illustrated rotor blade 36 includes a leading edge(abbreviated as “LE” in FIG. 2), a trailing edge (abbreviated as “TE” inFIG. 2), and an outer tip located radially adjacent treated region 30 ofengine casing 24. Grooves 34 can be continuous or interrupted. Infurther embodiments, a different groove configuration can be formed inregion 30, such as axially-extending grooves or skewed grooves. Asimilar type of casing treatment can also be applied to region 32 shownin FIG. 1 and surrounding rotor 18(f). Alternatively, a different typeof SEFs can be applied to region 30 and/or region 32.

FIG. 3 is an isometric cross-sectional view of a second, limited portionof multistage GTE compressor 10 to which SEFs have further been applied.Specifically, FIG. 3 illustrates region 31 of multistage axialcompressor 10 in an implementation wherein the SEFs are realized asupstream injection features 40 (one of which can be seen). In this case,upstream injections feature 40 include a stator core duct 42 andin-bleed conduit 44, which injects a small percentage of bleed flow intostator 20(d) upstream of stall limiting rotor 18(e) during operation ofcompressor 10. In a preferred embodiment, the bleed in-flow is deflectedto the tips of rotor 18(e) for improved surge margin. The bleed flow canbe passive or controlled by a secondary flow system (not shown), whichcontrols the rate of stator hub injection. In further embodiments, adifferent type of upstream injection may be integrated into region 31 ofcompressor 10.

The pressure ratios sustainable by multistage GTE compressor 10 areadvantageously increased due to the presence of SEF-containing regions30-32 integrated into compressor 10. Specifically, by applying SEF toselected regions 30-32 corresponding to stall limiting rotors 18(a),18(e), and 18(f), the pressure ratio capability of multistage GTEcompressor 10 is improved. At the same time, the addition of SEFs atlocations corresponding to the rotors contained within intermediatecompressor stages 16(b)-16(d) would be detrimental to compressorperformance or would provide a limited performance benefit outweighed byadded cost. In effect, the application of SEFs has been optimized in thecase of multistage GTE compressor 10 (FIG. 1) such that performance gainis maximized, while production costs, the addition of weight, and otherpenalties are minimized. An exemplary process for optimizing compressorperformance through the selective application of SEFs to a multistageGTE compressor, such as compressor 10, will now be described inconjunction with FIG. 4.

FIG. 4 is a flowchart illustrating an exemplary method 50 for optimizingGTE compressor performance. Exemplary method 50 commences with theestablishment of an optimized SEF configuration for a multistage GTEcompressor, such as compressor 10 shown in FIG. 1 (PROCESS BLOCK 52).The SEFs configuration is “optimized” in the sense that SEFs are appliedto selected regions of the multistage GTE compressor targeted to boostthe stall margin capability of a specific subset of rotors identified as“stall limiting rotors.” To establish the optimized SEF configuration(PROCESS BLOCK 52), a plurality of engine speeds is first selected (STEP54, FIG. 4). The selected engine speeds are distributed across anoperational range of the gas turbine engine containing the compressorsection. The selected engine speeds range from a minimum engine speed toa maximum engine speed and may include any number of intermediate speedsbetween the minimum and maximum engine speeds. In an embodiment, theselected engine speeds may be separated by fixed intervals of 5% or 10%speed increments, wherein 100% is the engine speed at cruise. Thisexample notwithstanding, the selected engine speeds need not occur atfixed internals in all embodiments. In certain instances, ground idle orstart-up may be selected at the minimum engine speed, while the maximumselected engine speed may be equal to or greater than the maximumexpected operational speed of the engine.

Advancing to STEP 56 of exemplary method 50 (FIG. 4), at least one axialcompressor rotor is identified as the “stall limiting rotor” for eachselected engine speed. As indicated above, the “stall limiting rotors”are the axial compressor rotors that set compressor stall at theselected engine speeds. As indicated in FIG. 4, the stall limitingrotors can be identified by generating a compressor performance maputilizing a model of the multistage GTE compressor. The compressorperformance map can be a graph of axial pressure ratio (vertical axis)versus inlet corrected flow (horizontal axis) plotting the speed linesfor the multistage GTE compressor at each of the selected engine speeds.The term “axial pressure ratio” refers to the ratio of outlet pressureover inlet pressure at each axial compressor stage, while the term“corrected flow” refers to the mass flow rate through the compressorstage corrected to standard day conditions. An example of such acompressor performance map 60 is illustrated in FIG. 5. In thisparticular example, compressor performance map 60 contains speed linesgenerated for the selected engine speeds of 70%, 80%, 85%, 90%, 95%,100%, and 105% (wherein 100% is the engine speed at cruise). While thesespeed lines are shown on a single map for purposes of comparison, itwill be appreciated that a different map may be generated for each speedline in actual implementations of method 50.

Compressor performance map 60 shown in FIG. 5 can be generated utilizingeither a physical model or a virtual model of the multistage GTEcompressor. When a physical model is utilized, the model can be operatedat each selected engine speed, while the axial pressure ratio isgradually increased by, for example, modulating an exhaust valvesupplying airflow to the model. The axial pressure ratio can begradually increased at a given engine speed until compressor stall isreached, at which point the speed line corresponding to the testedengine speed terminates. Pressure measurements are taken during thisprocess at each of the axial compressor rotors and possibly at otherlocations along the compressor. Any suitable measurement equipment canbe utilized for this purpose including, but not limited to, highresponse equipment. The pressure measurements are then analyzed todetermine which rotor or rotors set stall at the tested engine speed.This process is repeated at the other selected engine speeds to identifythe stall limiting rotor for each of the selected engine speeds. Asimilar process is performed when a virtual model is utilized togenerate compressor performance map 60. In this case, a specializedcomputer program can be utilized to analyze the virtual model of themultistage GTE compressor. The computer program is utilized to generatea speed line for each of the selected engine speeds as previouslydescribed. When stall is reached at a given one of the selected enginespeeds, the data is analyzed to identify which rotor or rotors setsstall at the selected engine speed. In one embodiment, computationalfluid dynamic analysis is utilized to identify the stall limiting stagesby numerical instabilities; however, various other types of analysis canbe utilized to identify the stall limiting stages in furtherembodiments.

The process described above can thus be utilized to identify a stalllimiting rotor at each of the selected engine speeds. In keeping withthe foregoing example, and as indicated in FIG. 5, rotor R₁(corresponding to rotor 18(a) in FIG. 1) may be identified as the stalllimiting rotor for engine speeds 70%, 80%, 85%, and 90% (indicated bydouble-headed arrow 62 in FIG. 5). Rotor R₅ (corresponding to rotor18(e) in FIG. 1) may be identified as the stall limiting rotor forengine speed 95% (indicated by double-headed arrow 64 in FIG. 5).Finally, rotor R₆ (corresponding to rotor 18(f) in FIG. 1) may beidentified as the stall limiting rotor for engine speeds 100% and 105%(indicated by double-headed arrow 66 in FIG. 5). As will be describedmore fully below, SEFs may consequently be applied to a model ofcompressor 10 at locations corresponding to rotors 18(a), 18(e), and18(f), such as the locations identified in FIG. 1 by cross-hatchedregions 30-32. As further indicated in FIG. 5, a stall line 68 can beextrapolated for the compressor model by connecting and extending theupper terminal ends of the speed lines includes in compressorperformance map 60.

Turning next to STEP 70 of exemplary method 50 (FIG. 4), SEFs are nextapplied to the compressor model at locations corresponding to stalllimiting rotors identified during STEP 56. In the case of a virtualcompressor model, the SEFs can be applied analytically by utilizing thecomputer program to adjust the virtual model of the compressor.Alternatively, in the case of a physical compressor model, the SEFs canbe physically added to or implemented into the compressor model. Forexample, in embodiments wherein a physical test model having non-treatedremovable casing sections is used, the casing sections surrounding therotors of the stall limiting stages can be removed and replaced bytreated casing sections; that is, casing sections having grooves orother casing treatment features formed therein. Additional computeranalysis and/or additional flow testing can then be carried-out toanswer the following query, which is presented at STEP 72 of exemplarymethod 50 (FIG. 4): “Is a predetermined stall threshold surpassed ateach of the multiple engine speeds?” Specifically, in answering thisquery, a second or revised compressor performance map can be generatedbased upon the virtual or physical model after the SEFs have beenapplied to selected regions thereof. An example of such a revisedcompressor performance map that can be generated during STEP 72 (FIG. 4)is described below in conjunction with FIG. 6. The present examplenotwithstanding, it will be appreciated that an ideal stall thresholdneed not be achieved at each of the multiple engine speeds in allembodiments of method 50. Instead, in certain cases, the method mayproceed to STEP 86 (production of a multistage GTE compressor includingthe optimized SEF configuration) when a minimal, acceptable level ofstall margin is achieved at each of the multiple engine speeds.

FIG. 6 illustrates a revised compressor performance map 80 generatedduring STEP 72 of exemplary method 50 (FIG. 4). The improved stall lineof the compressor model is represented by dashed line 82 connecting theupper terminal ends of stall lines, which have been extended by virtueof the selective addition of SEFs during STEP 70 (FIG. 4). As may beappreciated by comparing improved stall line 82 to the original stallline 68 (also shown in FIG. 6 for comparison purposes), the stallcapability of the compressor model has improved across the entirety ofthe engine's operational speed range. Specifically, the speed line ateach of the selected engine speeds now extends to a higher axialpressure ratio before stall is reached, as generally represented by theupper segments of the speed lines located between original stall line 68and improved stall line 82. Also, at each of the selected engine speeds,a predetermined stall threshold (represented in FIG. 6 by markers 84)has now been surpassed. As a result, the inquiry posed at STEP 72 isanswered in the affirmative, and PROCESS BLOCK 52 is completed with theestablishment of an optimized SEF configuration. One or more multistageGTE compressor can now be produced to include the optimized SEFconfiguration (STEP 86), and method 50 concludes. Conversely, if theanswer to the query posed at STEP 72 is “NO,” method 50 returns to STEP56 and the above-described steps of identifying the stall limitingrotors, applying SEFs to selected locations corresponding to the stalllimiting rotors, and then retesting the compressor model are repeated.Finally, as noted above, the threshold for determining whether toadvance to STEP 86 from decision STEP 72 can be based upon whether aminimal acceptable stall margin is achieved at each selected enginespeed in alternative implementations of method 50.

The foregoing has thus provided methods for producing a multistage GTEcompressor wherein compressor performance is optimized through theselective application of SEFs to a locations corresponding to a numberof stall limiting rotors. By producing the compressor to include anoptimized SEF configuration, the stall margin of the compressor cangenerally be maintained, while aerodynamic loading is favorablyincreased. As a result, the pressure ratios sustained during operationof the compressor can be increased to enhance overall GTE performance.In contrast to other known methods of boosting compressor ratios, theforegoing SEF optimization process avoids adding further stages to thecompressor or increasing in the rotational speed over which themultistage GTE compressor operates. Furthermore, the selectiveapplication of SEFs to at locations corresponding to a selected subsetof stall limiting rotors does not incur performance penalties that mayotherwise result at certain compressor stages. Thus, by utilizing theforegoing method to identify selected compressor stages setting theoperability limit across the operating range of the compressor, SEFs canbe integrated into a minimum number of compressor stages, whilemaintaining the desired stall margin of the compressor across the entireoperating range of the GTE.

While at least one exemplary embodiment has been presented in theforegoing Detailed Description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing Detailed Description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention. It beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set-forth in the appendedclaims. Finally, numerical identifiers, such as “first” and “second,”have been utilized in this document to reflect an order of introductionof similar elements or features in at least some instances. Suchnumerical identifiers may also be utilized in the subsequent Claims toreflect the order of introduction therein. As the order of introductionof such elements or features may vary between the Detailed Descriptionand the Claims, the usage of such numerical identifiers may also varyaccordingly.

What is claimed is:
 1. A method for producing a multistage Gas TurbineEngine (GTE) compressor including a series of axial compressor stages,the plurality of axial compressor stages containing a total number ofrotors equal to n_(total), the method comprising: producing themultistage GTE compressor to include a plurality of stall enhancingfeatures (SEFs) applied at selected locations corresponding to a subsetof rotors equal to n_(enhanced); wherein 2≤n_(enhanced)<n_(total);wherein a first SEF in the plurality of SEFs is applied to a forwardaxial compressor stage of the multistage GTE compressor; and wherein asecond SEF in the plurality of SEFs is applied to a first aft axialcompressor stage of the multistage GTE compressor.
 2. The method ofclaim 1 wherein producing comprises producing the multistage GTEcompressor in accordance with an optimized SEF configuration determinedby: selecting a plurality of engine speeds distributed across anoperational speed range of an engine in which the multistage GTEcompressor is utilized; identifying one or more stall limiting rotors ateach of the selected engine speeds; and establishing the optimized SEFconfiguration in which the plurality of SEFs are integrated into themultistage GTE compressor at selected locations corresponding to thestall limiting rotors.
 3. The method of claim 2 wherein identifyingcomprises identifying the one or more stall limiting rotors based, atleast in part, upon numerical instabilities generated by computationalfluid dynamic analysis of a virtual model of the multistage GTEcompressor.
 4. The method of claim 2 wherein identifying comprisesidentifying the one or more stall limiting rotors at each of theselected engine speeds utilizing a physical model of the multistage GTEcompressor having non-treated removable casing sections.
 5. The methodof claim 2 wherein identifying comprises: plotting a speed line for eachof the selected engine speeds on a compressor performance map, whileincreasing the axial pressure ratio applied across a model of themultistage GTE compressor until stall is reached; and after reachingstall at each of the selected engine speeds, utilizing data gatheredfrom the model to determine which of the rotors contained within theseries of axial compressor stages is the stall limiting rotor for eachof the selected engine speeds.
 6. The method of claim 1 furthercomprising: selecting the first SEF to comprise a first casing treatmentfeature; and selecting the second SEF to comprise an upstream injectionfeature.
 7. The method of claim 6 wherein the multistage GTE compressorfurther comprises a second aft axial compressor stage, wherein themethod further comprises applying a third SEF in the plurality of SEFsto the second aft axial compressor stage, and wherein the third SEFcomprises a second casing treatment feature.
 8. The method of claim 7wherein producing comprises producing the multistage GTE compressorcomprises leading and trailing axial compressor stages, and wherein themethod further comprises: applying the first casing treatment feature tothe leading axial compressor stage; applying the second casing treatmentfeature to the trailing axial compressor stage; and applying theupstream injection feature at a location between the leading andtrailing axial compressor stages.
 9. The method of claim 1 whereinproducing comprises producing the multistage GTE compressor such thatn_(total)≥6, while n_(enhanced) is≥3.
 10. The method of claim 1 furthercomprising: selecting the first SEF to comprise grooves formed in aninterior of the engine casing circumscribing a rotor contained in theforward axial compressor stage; and selecting the second SEF to comprisea stator hub flow injection feature positioned upstream of a rotorcontained in the first aft axial compressor stage.
 11. A multistage GasTurbine Engine (GTE) compressor included in a gas turbine engine, themultistage GTE compressor comprising: an engine casing; a shaft mountedin the engine casing for rotation about a rotational axis; a series ofaxial compressor stages each containing a rotor mounted to the shaft andsurrounded by the engine casing; and a plurality of stall enhancingfeatures (SEFs) integrated into the series of axial compressor stages atlocations corresponding to a selected subset of rotors included in theseries of axial compressor stages; wherein the total number of rotorscontained within the series of axial compressor stages is equal ton_(total), wherein the number of rotors included within the selectedsubset of rotors is equal to n_(enhanced), and wherein2≤n_(enhanced)<n_(total); and wherein the series of axial compressorstages comprises: a first forward axial compressor stage to which afirst SEF in the plurality of SEFs is applied; and a first aftcompressor stage to which a second SEF in the plurality of SEFs isapplied.
 12. The multistage GTE compressor of claim 11 wherein the firstSEF comprises a first casing treatment feature, and wherein the secondSEF comprises an upstream injection feature.
 13. The multistage GTEcompressor of claim 11 wherein the series of axial compressor stagesfurther comprises a second aft compressor stage, and wherein theplurality of SEFs further comprises a third SEF applied to the secondaft compressor stage.
 14. The multistage GTE compressor of claim 13wherein the third SEF comprises a second casing treatment feature. 15.The multistage GTE compressor of claim 14 wherein the multistage GTEcompressor comprises leading and trailing axial compressor stages; andwherein the first forward axial compressor stage and the second aftcompressor stage comprise the leading and trailing axial compressorstages, respectively.
 16. The multistage GTE compressor of claim 11wherein n_(total)≥6, and wherein n_(enhanced) is≥3.
 17. The multistageGTE compressor of claim 11 wherein the series of axial compressor stagesfurther comprises: a second forward axial compressor to which theplurality of SEFs is not applied; and a second aft compressor stage towhich the plurality of SEFs is not applied.
 18. The multistage GTEcompressor of claim 11 wherein the first SEF comprises grooves formed inan interior of the engine casing circumscribing a rotor contained in thefirst forward axial compressor stage, and wherein the second SEFcomprises a stator hub flow injection feature positioned upstream of arotor contained in the first aft axial compressor stage.
 19. Amultistage Gas Turbine Engine (GTE) compressor included in a gas turbineengine, the multistage GTE compressor comprising: an engine casing; ashaft mounted in the engine casing for rotation about a rotational axis;a series of axial compressor stages, comprising: a forward axialcompressor stage containing a first rotor mounted to the shaft andsurrounded by the engine casing; and a first aft compressor stagecontaining a second rotor mounted to the shaft and surrounded by theengine casing; a plurality of stall enhancing features (SEFs),comprising: a first casing treatment feature disposed around the firstrotor; and an upstream injection feature positioned upstream of thesecond rotor within a flow field thereof.
 20. The multistage GTEcompressor of claim 19 wherein the series of axial compressor stagesfurther comprises a second aft axial compressor stage adjacent the firstaft axial compressor stage, the second aft axial compressor stagecontaining a third rotor mounted to the shaft and surrounded by theengine casing; and wherein the plurality of SEFs further comprises asecond casing treatment feature disposed around the third rotor.